1. Field of the Invention
This invention relates to push-pull amplifiers, and in particular to push-pull amplifiers having active devices connected to coplanar transmission lines having coplanar conductors formed on a base substrate.
2. Related Art
Because GaAs integrated circuits are comparatively expensive, it is common to make microwave and millimeter (mm) wave circuits as hybrid circuits. The active devices that require the use of GaAs are fabricated on GaAs chips which are then mounted on a motherboard or base substrate made of a less expensive material, such as silicon, Al.sub.2 O.sub.3, BeO, and AIN.
Conventional circuits having a plurality of active devices are made by fabricating a separate integrated circuit or chip for each of the active devices. Circuit metalization and passive devices are printed on the base substrate and each chip is then mounted at an assigned site on the base substrate. The integrated circuit on the chip can be very simple, such as a single FET. It may also be more complex, incorporating a variety of devices to provide an overall function, such as is provided by an amplifier.
A complex circuit may require that numerous such chips be made and mounted. The resultant requirement for individual handling of small chips also tends to make the fabrication process somewhat costly. Alternatively, when a chip has a complex circuit, it is more expensive to make since it requires a larger GaAs substrate than its more simple cousin, and the benefits of hybrid circuit structure are not as fully realized.
There is thus a need for a method of hybrid circuit construction, and thereby a hybrid circuit structure that, when applied to microwave and mm-wave circuits, has reduced size and is simple to fabricate, thereby providing for efficient fabrication at reduced cost.